1. Field of the Invention
This invention relates to a device for labeling and identifying x-ray films. Specifically, it relates to an identification tape that can be affixed to an x-ray film cassette. More specifically, it relates to an identification tape that can be adhesively affixed to such an x-ray film cassette. Even more specifically, the invention relates to an identification tape onto which information can be written--either manually or mechanically. More particularly, the invention relates to an identification tape that is capable of permanently transferring such information to the x-ray film in the cassette once the film is exposed. Still more particularly, the invention relates to an identification tape that can transfer either a direct image or a mirror image of such information to the x-ray film. Finally, the invention relates to collections of such tapes wherein different sizes or radiopacities are distinguishable from one other by color coding.
2. Description of the Prior Art
Efficient record keeping is essential in the medical arts. One must be able to readily and accurately identify the results of diagnostic studies of a patient. Particularly with x-rays, not only is there an immediate need to positively identify the patient with the x-ray film, but such identification must still be possible long after the film has been exposed. Unless the film itself is marked or labeled, there is a possibility that the film and the identification means will ultimately be separated and the unlabeled x-ray film will be misplaced and/or misidentified.
A number of prior-art devices have been developed to label x-ray films with patient information. One particular approach is to place a labeling device--such as a plaque or tape--on the surface of a film cassette and between the radiation source and the film. Such labeling devices usually include a layer of radiopaque material that prevents exposure of the underlying film. When sufficient pressure is applied, the layer of radiopaque material can be broken or thinned by inscribing information--either mechanically or manually--on the labeling device. X-rays can then pass through the interrupted radiopaque layer and reach the film underneath, exposing it in a pattern corresponding to the inscription made on the plaque.
Buckley (U.S. Pat. No. 2,120,064; issued 1938 (hereinafter referred to as '064)) describes a plaque to be placed on an x-ray film cassette during exposure. The plaque has a cover sheet of yieldable material such as cellophane and a backing material coated with a material impermeable to x-rays. The cover sheet yields to the pressure of writing with a "suitable stylus" and the layer of radio-impermeable material is interrupted wherever the stylus has been used to inscribe information. The impermeable material used in the Buckley '064 device may be either lead or a lead salt, applied either in sheet form or by dusting an adhesive with such materials in powdered form. Alternatively, a thick paste of a lead compound such as "white lead"--i.e., lead oxide--may be spread evenly on the backing sheet. A translucent cellophane cover sheet allows the information inscribed on the radiopaque layer to be visually inspected. This device is prone to failure, however, when either the pressure applied by the stylus is insufficient to deform the underlying radiopaque material or where the cover sheet is "unduly thick."
A second identification plaque described by Buckley (U.S. Pat. No. 2,162,420; issued 1939 (hereinafter referred to as '420)) replaces the cover sheet of the earlier Buckley ('064) plaque with a cover layer of metal powder--preferably aluminum--that is transparent to x-rays. A layer of plastic radiopaque material containing white lead, glycerine, and a drying agent is applied to a backing member and the metal powder is dusted thereon. Excess powder is removed and the edges of the plaque are then painted with ordinary paint of unspecified color. An inscribing stylus penetrates both the metallic powder cover layer and the plastic material to contact a backing layer. Penetration of the plastic radiopaque layer produces an image of the inscription on the underlying film when the film is exposed to x-rays. The Buckley '420 device permits the radiopaque layer to be deformed more easily, but does not address the problem of visibility of the information inscribed on that layer.
Mika et al. (U.S. Pat. No. 3,790,802; issued 1974) describes a marker in which the inscribable surface is a foil of either indium, indium-lead alloy, or indium-tin alloy. The foil layer is applied to a paper support. The outer surface of the indium layer can be coated with a "bright, specifically white layer" to provide an easily inscribable area and improve the visibility of any writing on the marker. Neither markers of varying sizes and radiopacities nor an incscribable layer having a color other than white are contemplated by Mika et al. The white inscribable layer described therein does not provide a means of distinguishing differently-sized markers, or markers having different radiodensities.
The film identification device of Jackson (U.S. Pat. No. 3,917,952; issued 1975) has an outer sheet of material--such as paper or roughened polyethylene--that is capable of being easily marked by a pen or a pencil. A thin sheet of lead is typically used as the radiopaque material in this device, although finely divided lead oxides or barium sulfates may be used as well. The device, which includes additional backing sheets, is adhesively affixed to the film. Markers of various sizes and radiopacities were not addressed by Jackson.
Hurwitz (U.S. Pat. No. 4,764,948; issued 1988) describes an x-ray marking device in which the film can be labeled using a ball point pen, typewriter, or other types of mechanical marking instruments. The device includes a flexible substrate, a foil layer of fracturable radiopaque material overlying a soft material, such as polyester or plastic, that is transparent to x-rays, and a single adhesive layer covered by a peelable shield. Once the information is impressed upon the marking device, the shield is removed from the adhesive and the marking device is attached to the film cassette. The radiopaque material in the Hurwitz device is preferably lead or tin. A printable layer of titanium-white paint is applied over the layer of radiopaque material in order to improve the visibility of the information being imprinted onto the fracturable radiopaque layer. Means for differentiating among markers of various sizes are not addressed. The Hurwitz marking system permits a mirror image of the information inscribed on the device to be transferred to the film. Such a mirror image is properly oriented when viewed form the side of the film opposite from the x-ray source. When affixed to a film cassette, the Hurwitz marking device, because it has a single adhesive layer adjacent to the blocking area, is susceptible to hinging or flopping downward when the cassette is vertically deployed.
As mentioned above, each of the prior-art devices for marking x-ray films suffer from several disadvantages. For one, many such marking devices use a metallic foil as the radiopaque material. A considerable amount of pressure is often necessary to sufficiently `thin` such foils such that the underlying film will be sufficiently exposed and the information transferred. When such information is handwritten upon such markers, the pressure applied to the foil may be insufficient to thin it.
Another problem associated with the prior-art marking devices is the readability of what has been written on the surface of the marker (as opposed to reading the message that ends up on the film). If the information cannot be read, its accuracy cannot be ensured. Attempted solutions to this problem have included coating the radiopaque material--frequently a metal foil--with titanium white paint or covering it with a cover sheet of cellophane or smooth plastic. Neither of these approaches holds pencil marks or ink well, and any information written thereon is difficult to read.
Another limitation of the prior-art marking systems relates to the method used to read the exposed x-ray film. In some areas of medicine--such as mammography--it is customary to view the `back,` (i.e., the glossy side) of the film. To anticipate this type of use, it is helpful to transfer a mirror image of the information to the film. None of the prior-art systems provides a means for securely attaching the identification marker to the film cassette when the cassette is vertically oriented such that a mirror image of the information written on the marker is transferred to the film. An additional shortcoming of the prior-art film marking systems is their failure to facilitate the use of markers of different sizes and radiopacities. In practice, the x-ray film used varies in size from one application to another within different fields of medicine. It is therefore important to have film markers of various sizes and a simple means for distinguishing between them. Furthermore, depending on the purpose or body part being x-rayed and the purpose of the x-ray--i.e., dental, chest, mammogram--the x-ray energy may vary as well. Consequently, it may be desirable to have markers with different, but well-defined, radiopacity ranges. Simply tailoring the thickness of a metal foil to achieve this may be difficult. Thin foils that could be possibly used in a less radiodense marker would be susceptible to tearing. Conversely, a thick film used in a marker of high radiopacity would be extremely difficult to thin with the amount of force normally applied by a stylus. In addition, the existence of markers having different ranges of radiopacity gives rise to the need to be able to readily distinguish markers having one value of radiopacity from markers having another such value.
The prior-art systems thus fail to provide a means for marking x-ray films that addresses the problems described above. Therefore, what is needed is a device for marking x-ray films that allows information to be handwritten on a flexible x-ray marking tape in such a way that it is then reliably transferred to an underlying x-ray film. What is also needed is such a marking tape that allows the user to easily see what has been written on the tape itself What is further needed is such a marking tape that will remain securely affixed to a film cassette regardless of cassette orientation. In addition, what is needed is such an x-ray marking tape that is capable of transferring a mirror image of the information inscribed on the tape. What is still further needed is to have a variety of such marking tapes of different radiopacities and sizes, coded according to their size and/or radiopacity, respectively.